Micro-scale resonators (e.g., micro-cantilever resonators) can be used in many applications such as chemical sensing, biological sensing, atomic force microscopy, and other measurement applications. However, a limiting factor in the precision of measurements made with such sensors is the quality factor (Q) of a given resonator. A quality factor for a resonant sensor can be determined as the resonant frequency of the resonator divided by the width of that resonant frequency peak of the resonator. Further, to obtain specificity to a desired analyte, these resonant sensors can include surface coatings that not only selectively bind the desired analyte, but also cause the desired analyte to bind in such a way that it affects (e.g., linearly affects) a property to be measured (e.g., resonant frequency).
In such resonant sensors, in order to have a mass ratio between the cantilever and an adsorbed chemical or biological analyte (e.g., bound to a surface coating) sufficient for accurate sensing, it is preferable that the resonator (sensor) be thin (e.g., have a low aspect ratio). However, in order to have a high quality factor, it is preferable that the resonator be thick (e.g. have a high aspect ratio). These opposing goals lead to making a tradeoff between a low aspect ratio and a high aspect ratio in current resonant sensor devices, such as may be determined for a desired application. Additionally, current implementations are limited in achieving mass ratios (e.g., sensor to bound analyte) that are sufficient for accurate sensing by a surface area of the sensor that is available for binding a desired analyte. The consideration can also factor into the aspect ratio tradeoff decision.
Additionally, while certain resonant sensors (e.g., microcantilever sensors) have demonstrated mass detection limits down to 7 zeptograms (10−21 g) in vacuum, such mass detection sensitivities in fluid environments have not been achieved for these resonant sensors due, at least in part, to fluid damping causing low quality factors, which can result, in part, from the aspect ratio tradeoff discussed above.